Heat exchangers or radiators are known of the type in which are provided two circuits for the passage of a liquid to be cooled, said circuits being controlled by a valve sensitive to the liquid temperature, so that when the engine cooling liquid temperature is low (for example when starting after a prolonged stop), the valve controls the opening of one of the circuits through which the liquid returns directly to the engine without passing through the exchanger or flows only through a small portion of the exchanger, so that the increase of temperature of the engine is quick and, when the engine is hot, the valve controls the passage of the liquid in the other circuit, in order to have it flow in the exchanger so as to cool it down.
In such known devices, the valve is either exterior the exchanger, thereby involving special connections with the engine cooling circuit, or integrated to a radiator water box and is then out of access unless the water box is completely disassembled. The construction, the mounting and the connection of the radiator is therefore complex and its cost price is increased.